My right front tire pretty suddenly wore out on the outer tred row. The
truck was pulling right. I put the never used spare on the right front
and the truck wanted to go slightly LEFT. Had the alignment checked and
everything supposedly was within specs, except cross camber which was
.7 (left +.5/right -.2) with a notice in red that this is an unsafe
condition. Camber is not adjustable. Place that checked alignment said
pressures were wrong and changed them to 35--but the placard says 41,
and the 245/75/16 tires say max 44. Steering felt heavy and definitely
pulling left. I ran pressure back up to 41 and it felt normal.

Took it to another place to check alignment and their cross camber was
still .7, but shifted more to the negative--left +.4 / right -.3. The
rest of the readings were within specs but considerably different than
the first place.

I had a near empty gas tank, but 210 pounds of sand in short box bed
over rear axle for ice stability. Also noticed left front of vehicle
seemed about one inch lower than right, while left rear was only about
1/4 in lower. And, I couldn't understand how - .3 would cause outside
tred wear--I thought it would be inside wear.

So my questions are:
Is this really unsafe?
Where does camber come from--control arms? The front drive mechanism?
(There must be a way to change it if necessary)
Did sand change the alignment?
Why is the left front low?

I have the service manual but it doesn't really say a lot about this.
Any help would be appreciated.